1. Field of the Invention
The present invention relates to an optical reader for optically reading an information pattern representing coded data, and particularly to an optical reader suitable to read a two-dimensional information pattern representing coded data.
2. Description of the Related Art
Recently, as a two-dimensional information pattern representing coded data, otherwise known as a tessellated information pattern, in which black zones and white zones are two-dimensionally arranged to represent the coded data, has been proposed. An optical reader for reading the coded data from the tessellated information pattern and for decoding the coded data has also been developed. The optical reader is frequently a hand held-type reader, having a reading head including a hollow box-like head casing with a bottom opening formed in a bottom wall thereof which defines a reading area. The reading head also includes a two-dimensional CCD (charge coupling device) image sensor associated with an image formation lens, which is located in a hole formed in a top wall of the head casing. The reading head also includes a light source incorporated in the top wall of the head casing, and the reading area is illuminated by the light source.
For example, when a two-dimensional information pattern is placed on an article, the optical reader is positioned relative to the article such that the information pattern is encompassed in the reading area of the reading head thereof. The information pattern is then illuminated by the light source, and an image of the pattern focuses on a light receiving surface of the image sensor by the image formation lens, whereby the focussed image is converted into image signals by the image sensor. The image signals are read out from the image sensor, and processed for conversion into digital data. The digital data is further processed for decoding, and the decoded data is temporarily stored in a memory. When the decode process is complete, the optical reader produces a visual indication or audio indication, whereby a user is advised that the optical reading of the information pattern has been properly carried out. If necessary, the decoded data is read out from the memory, and is fed to, for example, a host computer in communication with the optical reader.
Before the proper optical reading of the two-dimensional information pattern by the image sensor can occur, the reading head of the optical reader must be positioned properly with respect to the article such that the information pattern is encompassed completely by the reading area of the recording head. Nevertheless, a user cannot visually confirm whether or not the information pattern is encompassed within the reading area of the reading head. Namely, the user cannot known whether or not the proper optical reading of the information pattern can be carried out until the optical reader produces the visual indication or audio indication. Accordingly, if the information pattern is not completely encompassed within the reading area of the recording head, i.e., if the optical reader does not produce the visual indication or audio indication, the user must repeat the process after the reading head is re-positioned with respect to the information pattern.